1. Field of Invention
The present invention relates to an engine compartment structure of a vehicle for introducing cool air into an intake air system of the engine.
2. Description of the Related Art
Recently, supply of a large amount of air to engine combustion chambers for higher power performance is required from automotive engines. However, intake air in an engine is heated in the engine compartment and the temperature of the air rises before the air is sucked into the combustion chambers. When the temperature of the intake air introduced into the chambers rises, the air density is reduced, the weight of the intake air is reduced, and the air filling efficiency of the chambers is also reduced. Thus, the engine power is reduced and engine knocking occurs.
FIG. 12 is a schematic diagram showing a conventional engine compartment structure of a vehicle for introducing cool air into an intake air system of the engine. In FIG. 12, an air intake port 2 of a combustion engine I is located behind a first headlamp 3 in the engine compartment. A pair of cooling fans 5 and 5a are mounted on a rear side of a radiator 4 at substantially the same height, and the cooling fans rotate counterclockwise, as seen from the engine side. The cooling fans 5 and 5a shown at the bottom of FIG. 12 are depicted as if they were viewed through a radiator 4 when they were seen from the front of a vehicle, and arrows indicate rotational directions of the cooling fans 5 and 5a mounted on the radiator 4, for ease of understanding. The number of revolutions per minute and the blade length for each of the cooling fans 5 and 5a are the same. The intake air flowing into the air intake port 2 is sucked into combustion chambers of the engine 1 via an intake duct 6, an air cleaner 7, an intake pipe 8, a surge tank 9 and an intake manifold 10, in that order. A transmission 11 is provided on the right side of the engine 1 as seen from the front of the vehicle. Above the transmission 11, there is a space, as the height of the transmission 11 is lower than that of the engine block 1. The radiator 4 is covered with an under cover 12. Fresh air FA flows into the engine compartment from outside after passing through a space behind a second headlamp 3a located opposite to the first headlamp 3 and the air intake port. However, after passing through the radiator cooling fans 5 and 5a heated air HA turns around toward the air intake port 2, and raises the temperature of the intake air. This results in reduced air filling efficiency in the combustion chambers of the engine.
In order to solve the above problem, a structure that restricts temperature increases of air introduced into an intake air system of an engine is disclosed in Japanese Unexamined Patent Publication No. 5-1634. According to the invention, the temperature of the air introduced into the intake air system from outside via an air intake port and an intake duct decreases, so that the air filling efficiency to the combustion chambers of the engine can be improved. To accomplish this, a baffle plate is provided in the structure in such a way as to extend a fan shroud of a radiator toward the rear of a car body and to intentionally open the air intake port of the intake duct toward the opposite side of the radiator, thereby preventing heated back wind passing through the radiator cooling fans from being introduced into the intake air system of the engine.
However, according to the invention disclosed in Japanese Unexamined Patent Publication No. 5-1634, a baffle plate must be provided. Therefore, additional expense for the baffle plate and for the man hours for assembling the baffle plate are required.